The copolymerization of methyl 2,3-difluoroacrylate with .alpha.,.beta.,.beta.-trifluorostyrene is known (q.v. Tevlina A.S. et al., VINITI 127-81 (1981)). The properties of the copolymers formed were not published.
A transparent molding compound containing monomer groups derived from 2,3-difluoroacrylic acid of fluorinated, chlorinated or brominated polycyclic alcohols has also been disclosed (q.v. DE 3707923). Nothing is known of the properties of these compounds.
Transparent thermoplastic molding compounds which are derived from (meth)acrylates of cyclic alcohols are disclosed in EP-A 282,019. The refractive indices of these polymers are about 1.43, frequently even above 1.52.
Furthermore, an optical material is known which consists of polymeric 2-fluoroacrylic acid esters of, in particular, aliphatic alcohols, it being possible for said esters to contain deuterium atoms both in the alcohol component and in the .beta.-position of the 2-fluoroacrylic acid component (q.v. EP 128517). These polymers have refractive indices of between 1.45 and 1.60 and glass transition temperatures of between 100 and 200.degree. C. and are used as the core material for optical fibers (beam waveguides).
The preparation and properties of polymers of fluoroalkyl 2-fluoroacrylates are also known (q.v. EP 128516). The polymers are prepared by free radical-initiated bulk, solution or suspension polymerization of the monomers in the presence of a chain transfer agent at a temperature of between 0.degree. and 100.degree. C. They have refractive indices of between 1.36 and 1.44 and softening points of between 80.degree. and 140.degree. C.
These polymers still contain two hydrogen atoms in the acid component and perhaps further hydrogen atoms in the alcohol component, thereby impairing the transparency of the polymers in the visible and near infrared regions of the electromagnetic spectrum.
Moreover, it has already been proposed to use beam waveguides of poly(2-fluoroacrylic acid esters) in the core and either poly(2,3-difluoroacrylic acid esters) or copolymers of TFE, perfluoroalkyl vinyl ethers and .omega.-alkoxycarbonyl (perfluoroalkyl vinyl ethers) in the sheath of a beam waveguide.